This can have various reasons:

1. If you are using an external camera please check that it is properly connected and installed
   
2. Check that the volume control on your computer is set correctly (you may need to turn on the sound for your microphone or speakers)
   
3. Allow access to your camera and microphone at the start of your appointment for the duration of the conversation
   
4. Make sure that no other program or page are accessing the camera or speakers at the moment. If they do, log out and close all programs. Restart your browser and log in again.
   
5. If there are several microphones connected (e.g. integrated in camera and connected headset), please allow access to your preferred device.